A conventional receiver in a multi-channel optical communication system typically includes a clock recovery circuit designed to operate at a particular predetermined bit rate. The receiver is therefore bit-rate specific. Performance monitoring of a given channel signal in the receiver is generally done only after the channel signal data has been completely recovered, and thus after a bit-rate specific clock recovery process. This presents a significant problem in applications such as wavelength division multiplexed (WDM) optical networks in which the transmission medium is generally bit-rate independent. More particularly, the nodes of such a network often do not have any information regarding the bit rate of particular channel signals which are routed through them. As a result, it is generally not possible to monitor the performance of a channel signal at a network node without including the above-noted bit-rate specific receiver circuitry at that node.
Including such bit-rate specific circuitry for each channel signal at each node of a network would substantially increase the cost and complexity of the network, and is therefore not a viable solution for most practical applications. Unfortunately, there are apparently no suitable alternative techniques which may be used to provide a bit-rate independent channel signal monitoring capability in a node of an optical network. A need therefore exists for a device which can identify a channel signal and measure its performance at a node of an optical network, without requiring prior information about the specific signal bit rate, without completely recovering the channel signal data, and thus without the need for bit-rate specific clock recovery circuitry.